High Energy Proton-nucleus Collisions Research Articles

Heavy Flavor Production from the Color Glass Condensate in pA Collisions

Heavy quark production in high-energy proton-nucleus (pA) collisions is described in the framework of the Color Glass Condensate, where multiple scattering and parton saturation effects are treated in a consistent manner with the correlators of Wilson lines in the nuclear target. We show results for heavy quark production at RHIC and LHC energies, and comment on the case of nucleus-nucleus collisions.

Production ofqq¯pairs in proton-nucleus collisions at high energies

We calculate production of quark-antiquark pairs in high energy proton-nucleus collisions both in the quasi-classical approximation of McLerran-Venugopalan model and including quantum small-$x$ evolution. The resulting production cross section is explicitly expressed in terms of Glauber-Mueller multiple rescatterings in the classical case and in terms of dipole-nucleus scattering amplitude in the quantum evolution case. We generalize the result of one of us (K.T.) beyond the aligned jet configurations. We expand on the earlier results of Blaizot, Gelis and Venugopalan by deriving quark production cross section including quantum evolution corrections in rapidity intervals both between the quarks and the target and between the quarks and the projectile.

Violation of [formula omitted] factorization in quark production from the Color Glass Condensate

We examine the violation of the kT factorization approximation for quark production in high energy proton-nucleus collisions. We comment on its implications for the open charm and quarkonium production in collider experiments.

Quark production in high-energy proton-nucleus collisions

In this note, we discuss the problem of quark-antiquark pair production in the framework of the color glass condensate. The cross-section can be calculated in closed form for the case of proton-nucleus collisions, where the proton can be considered to be a dilute object. We find that $k_\perp$ -factorization is broken by rescattering effects.

Erratum: Inclusive two-gluon and valence-quark–gluon production in DIS andpAcollisions [Phys. Rev. D70, 114017 (2004)

We calculate production cross sections of a forward quark-gluon pair and of two gluons at mid-rapidity in Deep Inelastic Scattering and in high energy proton-nucleus collisions. The calculation is performed in the framework of the Color Glass Condensate formalism. We first calculate the cross sections in the quasi-classical approximation, which includes multiple rescatterings in the target. We then proceed to include the effects of non-linear small-x evolution in the production cross sections. It is interesting to note that our result for the two-gluon production cross section appears to be in direct violation of AGK cutting rules, which is the first example of such violation in QCD. The calculated quark-gluon and gluon-gluon production cross sections can be used to construct theoretical predictions for two-particle azimuthal correlations at RHIC and LHC (I^{p(d)A}) as well as for Deep Inelastic Scattering experiments at HERA and eRHIC.

Inclusive two-gluon and valence-quark-gluon production in DIS andpAcollisions

We calculate production cross sections of a forward quark-gluon pair and of two gluons at midrapidity in deep inelastic scattering and in high energy proton-nucleus collisions. The calculation is performed in the framework of the color glass condensate formalism. We first calculate the cross sections in the quasiclassical approximation, which includes multiple rescatterings in the target. We then proceed to include the effects of nonlinear small-$x$ evolution in the production cross sections. It is interesting to note that our result for the two-gluon production cross section appears to be in direct violation of Abramovsky-Gribov-Kanchelli cutting rules, which is the first example of such violation in QCD. The calculated quark-gluon and gluon-gluon production cross sections can be used to construct theoretical predictions for two-particle azimuthal correlations at the Relativistic Heavy Ion Collider and LHC (${I}^{p(d)A}$) as well as for deep inelastic scattering experiments at the Hadron Electron Ring Accelerator and the Electron-Relativistic Heavy Ion Collider.

High energy pA collisions in the color glass condensate approach I: gluon production and the Cronin effect

We study gluon production in high energy proton–nucleus collisions in the semi-classical framework of the color glass condensate. We develop a general formalism to compute gluon fields in covariant gauge to lowest order in the classical field of the proton and to all orders in the classical field of the nucleus. The use of the covariant gauge makes the diagrammatic interpretation of the solution more transparent. k ⊥ -factorization holds to this order for gluon production—our results for the gluon distribution are equivalent to the prior diagrammatic analysis of Kovchegov and Mueller. We also show that these results are equivalent to the computation of gluon production by Dumitru and McLerran in the Fock–Schwinger gauge. We demonstrate how the Cronin effect arises in this approach, and examine its behavior in the two extreme limits of (a) no small- x quantum evolution, and (b) fully saturated quantum evolution. In both cases, the formalism reduces to Glauber's formalism of multiple scatterings. We comment on the possible implications of this study for the interpretation of the recent results on deuteron–gold collisions at the Relativistic Heavy Ion Collider (RHIC).

Cronin effect and energy conservation constraints in high energy proton-nucleus collisions

We estimate the Cronin effect in pA collisions at the CERN LHC and at RHIC, using a Glauber-Eikonal model of initial state multiparton interactions. For a correct determination of the initial parton flux, we upgrade the model cross section, taking carefully into account all kinematical constraints of each multi-parton interaction process. As compared with previous results, derived with approximate kinematics, we obtain a softer spectrum of produced partons, while improving the agreement of the model with the recent measurements of neutral pions production in d+Au collisions at sqrt(s)=200 AGeV.

Dilepton production from the color glass condensate

We consider dilepton production in high energy proton-nucleus (and very forward nucleus-nucleus) collisions. Treating the target nucleus as a Color Glass Condensate and describing the projectile proton (nucleus) as a collection of quarks and gluons as in the parton model, we calculate the differential cross section for dilepton production in quark-nucleus scattering and show that it is very sensitive to the saturation scale characterizing the target nucleus.

Photon production in high energy proton-nucleus collisions

We calculate the photon production cross-section in $pA$ collisions under the assumption that the nucleus has reached the saturation regime, while the proton can be described by the standard parton distribution functions. We show that due to the strong classical field $O(1/g)$ of the nucleus, bremsstrahlung diagrams become dominant over the direct photon diagrams. In particular, we show that $\gamma-$jet transverse momentum spectrum and correlations are very sensitive to gluon saturation effects in the nucleus.

Drell-Yan and J/ψ production in high energy proton-nucleus and nucleus-nucleus collisions

The distributions of outgoing protons and charged hadrons in high energy proton-nucleus collisions are described rather well by a linear extrapolation from proton-proton collisions. This linear extrapolation is applied to precisely measured Drell-Yan cross sections for 800 GeV protons incident on a variety of nuclear targets. The deviation from linear scaling in the atomic number A can be accounted for by energy degradation of the proton as it passes through the nucleus if account is taken of the time delay of particle production due to quantum coherence. We infer an average proper coherence time of 0.4±0.1 fm/c. Then we apply the linear extrapolation to measured J/ψ production cross sections for 200 and 450 GeV/c protons incident on a variety of nuclear targets. Our analysis takes into account energy loss of the beam proton, the time delay of particle production due to quantum coherence, and absorption of the J/ψ on nucleons. The best representation is obtained for a coherence time of 0.5 fm/c, which is consistent with Drell-Yan production, and an absorption cross section of 3.6 mb, which is consistent with the value deduced from photoproduction of the J/ψ on nuclear targets. Finally, we compare to recent J/ψ data from S+U and Pb+Pb collisions at the SPS. The former are reproduced reasonably well with no new parameters, but not the latter.

Drell-Yan and J/$psi; production in high energy proton-nucleus and nucleus-nucleus collisions*1

Drell-Yan and J/$psi; production in high energy proton-nucleus and nucleus-nucleus collisions*1

J/ ψ production and absorption in high energy proton-nucleus collisions

Measured J/ ψ production cross sections for 200 and 450 GeV/c protons incident on a variety of nuclear targets are analyzed within a Glauber framework which takes into account energy loss of the beam proton, the time delay of particle production due to quantum coherence, and absorption of the J/ ψ on nucleons. The best representation is obtained for a coherence time of 0.5 fm/c, previously determined by Drell–Yan production in proton-nucleus collisions, and an absorption cross section of 3.6 mb, which is consistent with the value deduced from photoproduction of the J/ ψ on nuclear targets.

Coherence Time in High Energy Proton-Nucleus Collisions

Precisely measured Drell-Yan cross sections for 800 GeV protons incident on a variety of nuclear targets exhibit a deviation from linear scaling in the atomic number A. We show that this deviation can be accounted for by energy degradation of the proton as it passes through the nucleus if account is taken of the time delay of particle production due to quantum coherence. We infer an average proper coherence time of 0.4 +- 0.1 fm/c, corresponding to a coherence path length of 8 +- 2 fm in the rest frame of the nucleus.

Charmonium production in proton-nucleon and proton-nucleus collisions

Systematic nuclear effects discovered in the production ofJ/ψ particles in high-energy proton-nucleus collisions cannot be explained within the conventional picture in which a heavy color singlet\(Q\bar Q\) pair, after its production, experiences multiple scattering from nucleons of the residual nucleus. We propose to take into account color octet intermediate states formed in the primary production of the heavy-quark pairs. Using a perturbative QCD analysis we study the microscopic production mechanism for\(Q\bar Q\) pairs through gluon-gluon fusion with subsequent color neutralization in a strongly interacting medium. The influence of the surrounding matter on this process is investigated.

Phenomenology of xF Dependence of Quarkonium Production in Proton-Nucleus interactions11The project supported partly by National Natural Science Foundation of china

We present a phenomenological study of the xF dependence of quarkonium production in high-energy proton-nucleus collisions. The xF dependence of comover contributions is introduced to account for the observed quarkonium suppression at low xF. Combining comover contributions, nuclear shadowing effect, energy loss mechanism and nuclear absorption together we reproduce the overall xF dependence of E772/E789 data.

Polarization of $$\Sigma ^ + and \bar \Sigma ^ - $$ hyperons produced in high-energy proton-nucleus collisionshyperons produced in high-energy proton-nucleus collisions

We have measured the polarization of\(\Sigma ^ + and \bar \Sigma ^ - \) hyperons at 375 GeV/c, produced by 800 GeV/c protons on a copper target, atpT up to 1.7 GeV/c. The polarization behaviour is compared and contrasted with that of other hyperons and antihyperons in similar kinematic regions.

Pomeron-nucleus interactions

The recently measured cross-sections for diffractive dissociation of nuclei in high-energy proton nucleus (pA) collisions show a strikingA1/3 dependence on the target massA. Such a dependence emerges from an optical model which incorporates a simple mechanism to produce the absorption fluctuations required for inelastic diffraction. The observed momentum transfer (t) dependence of the differential cross-section, dσ/dt∝ exp(−B|t|), is described in terms of a correlation length\(R_F = \sqrt {2B} \) of the absorption fluctuations which turns out to be of the size of a nucleon. The excitation massM dependence, dσ/dM2∝M−2, is explained by a bremsstrahlung mechanism.

Enhancement of the K+/π+ Ratio in High-Energy Proton-Nucleus and Nucleus-Nucleus Collisions due to the Final State Interactions11The project supported by National Natural Science Foundation of China

The pion-meson secondary collisions with surrounding nucleons in the nucleus can influence the K+/π+ ratio. We calculate this effect in proton-nucleus and nucleus-nucleus collisions by the Glauber model and find that the final state interactions are important.

Target fragmentation in proton and heavy-ion induced reactions at high energies

Results on pseudorapidity distributions, azimuthal correlations, and on two particle interferometry for identified protons and pions measured in the target fragmentation region of high energy proton-nucleus and nucleus-nucleus collisions are presented. Full participation of the whole target nucleus is observed even for 200 GeV p + Au collisions. Incorporation of strong rescattering phenomena into string models, including pion absorption effects in excited target matter, provides a good description of most experimental data.